1. InDesign 19.0.1
2. Steps to reproduce: open an InDesign file with a placed PNG.
3. Expected result: file opens, no asterisk appearing next to file name.
4. Actual result: file opens, PNG re-renders in high quality, asterisk suddenly appears next to file name.

As of this morning, every time I open a file that has placed PNGs, InDesign flags the document as modified, with the asterisk and asks me if I want to save the document before closing, even I made zero edits. To give even more credence, it only happens when I navigate to a page that has a linked PNG file in it. If I open a file and there are no PNGs on the page, no asterisk (JPGs and other placed graphics are just fine). The minute I "page down" and hit a page that has a placed PNG, it "redraws/re-renders" the PNG (I have high quality previews turned on, and when I get to those pages, the PNGs look a little low-res at first; you can see the dark blue progress bar at the bottom appear as it redraws the preview and then the image looks better once the high quality preview is finished drawing) and then, BAM, asterisk appears. Nothing was modified other than InDesign redrawing/updating the preview.

I found some older forum topics and a previous bug report from 2018 (IIRC) in which that very thing was being investigated, which is what led me to figure out if that was the culprit for me, as well. It does appear to be so.